Process and apparatus for the mixing and direct emplacement of a two-component bone cement

ABSTRACT

A process and apparatus is disclosed for the mixing and direct emplacement of a bone cement formed from two components, one liquid and one powder, comprising the steps of storing the two components separately in a multichamber container, opening the liquid phase container within one of the said chambers which is not in communication with the outside atmosphere, setting up a negative pressure within the chamber containing the powder phase, causing aspiration of the liquid into the chamber containing the powder, mixing the two phases, compacting the paste obtained, injecting the paste into a cannula and extruding the paste with direct emplacement of the cement.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.07/621/847, filed Dec. 4, 1990 now Pat. No. 5,193,907.

The present invention relates to a process for the mixing and directemplacement of a bone cement formed from two components, one liquid andone powder, which components are kept separate until the cement isrequired for use, each component comprising a mixture of one or moremutually compatable components, and to apparatus for carrying out suchprocess.

Currently known systems for the preparation of bone cement include atleast one stage during which the liquid component, which ispredominantly based on a monomer, is able to disperse its highly toxicvapours into the environment. These vapours can then be inhaled by theoperator handling the cement during this stage with a consequentialserious hazard to the operators health if this operation is performedfrequently.

In most cases,the components of a bone cement are stored prior to use intwo different containers, such as for example sachets of plasticsmaterial for the powder component and glass vials for the liquidcomponent. Because of the very high reactivity of the liquid component,and its toxicity, its container must have special mechanical strengthproperties and be resistant to chemical attach by the liquid containedtherein.

When preparing the cement paste, the operator opens the vial and poursthe liquid into a container into which the powder component haspreviously been placed, or vice versa. The operator then mixes the twocomponents with a spatula, or places a cover fitted with an externallyoperable rotatory spatula on the container.

In both cases, vapour from the liquid component is left free to diffuse,and this can be inhaled by persons in its immediate vicinity.

Known mixing systems also have a further disadvantage associated withthe fact that certain operations bring components of the cement mixtureinto contact with the environmental atmosphere, in such a way that germspresent in the air can contaminate the components and can subsequentlyinfect the bone of the patient operated on when the cement is inposition.

An object of the invention is to provide a method for the preparationand direct emplacement of a bone cement formed from a solid and a liquidcomponent which is simple and practical, which requires no fixedequipment, such as suction hoods or centrifuging equipment, whichprovides a perfectly aseptic bone cement, which is homogeneous and hasminimum porosity, and which avoids releasing the toxic vapours of theliquid component into the environment.

According to the present invention there is provided a process formixing a bone cement formed from two components, one liquid and onepowder, which components are kept separate until the cement is requiredfor use, each component comprising a mixture of one or more componentswhich are mutually compatible, and if required, for delivering itdirectly in situ, such process comprising the following steps:

separately storing the two components which are to be mixed, within acontainer comprising a plurality of chambers aseptically isolated fromthe outside atmosphere;

opening the container for the liquid component within one of theaforesaid chambers which does not communicate with the outsideatmosphere;

creating a negative pressure in the chamber containing the powdercomponent;

said negative pressure causing suction of the liquid component into thechamber containing the powder component, the two chambers being keptisolated from the outside atmosphere.

mixing the two components by agitation of the container;

compacting the cement paste obtained by compressing same;

inserting, if required, a flexible cannula so as to direct the outflowof paste; and

extruding the paste by manual or mechanical or pneumatic action on aplunger, causing direct in situ emplacement of the cement.

Also according to the present invention there is provided an apparatusfor carrying out such process, said apparatus comprising a substantiallycylindrical hollow body, a cover which can be attached to the said body,said cover having an aperture or holecoaxial with the longitudinal axisof the body and a plunger consisting of a stem which can move axiallyinside the said hole and a head which together with body bounds thechamber which aseptically houses the powder component of the cement, inwhich said body has at its base and projecting outwardly a hollowcylindrical needle which can be closed off by means of a sealing plugand in which the plunger which can move within the cylindrical cavity ofthe said body has a cavity forming the chamber housing the container ofthe liquid component of the cement, fitted with means for breaking thecontainer which can be operated from outside the chamber itself and inwhich the chamber housing the powder component and the chamber housingthe container of the liquid component are placed by means of a pluralityof holes protected by a filter and located on the said head.

A first advantage of this invention derives from the fact that theprocess allows the two liquid and powder components of the bone cementto be mixed without hazardous inhalation of the toxic vapours of theliquid component by those present.

A second advantage derives from the fact that with the process accordingto the invention the paste is never directly handled by the operator andalways remains in an isolated aseptic environment before and duringdirect emplacement, and therefore the paste cannot be contaminated bygerms present in the ambient air and in the operating theatre.

Another advantage derives from the reduced porosity of the cementobtained with the process according to the invention. This reducedporosity also results in an improvement in the mechanical strengthproperties of the cement, in addition to improved homogeneity of thepaste.

A further advantage derives from the special simplicity and practicalityin use of the apparatus for implementing the process according to theinvention, and the possibility of constructing this apparatus withmaterials which permit single use. This apparatus therefore isappropriate for use in environments which are not very congenial, suchas for example field hospitals or any other environments not providedwith aseptic air.

The present invention will be further illustrated, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic exploded view, in partial cross-section ofapparatus according to the invention;

FIG. 2 is an imploded view, in partial cross-section, of the apparatusin FIG. 1 when ready for use;

FIG. 3 is a view impartial cross-section of the apparatus of FIG. 1during the stage immediately following breakage of the vial;

FIG. 4 is a view in partial cross-section of the apparatus of FIG. 1during the stage in which a negative pressure is created therewithin;

FIG. 5 is a view in partial cross-section of the apparatus of FIG. 1ready for delivery of the cement contained therein;

FIG. 6 is an imploded view in partial cross-section of a secondembodiment of apparatus according to the invention;

FIG. 7 is a view similar to that in FIG. 6 of a third embodiment of theinvention;

FIG. 8 is a view similar to that in FIG. 6 of a fourth embodiment of theinvention; and

FIG. 9 is a view similar to that in FIG. 6 of a fifth embodiment of theinvention.

FIG. 10 is a partial cross section of an apparatus according to theinvention including rotating mechanical means in the form of a couplinghead A arranged to be operatively connected to a locking chuck forextruding the cement past.

FIG. 11 is a partial cross section of an apparatus according to theinvention provided with rack and pinion mechanical means includinghandles which can be actuated through a ratchet gear, for extrudingcement paste.

FIG. 12 is a partial cross section of an apparatus according to theinvention including a pneumatic device comprising a compressed air inlettube to a compressed air source and in communication with an annularspace.

FIG. 13 is a partial cross section of a sealing plug including an innerfilter for use in communication with a sucking pump via an air suckingduct.

The process for the mixing and direct emplacement of a bone cementformed from two components, one liquid and one powder, which are keptseparate until the cement is ready for use includes the following steps:

separate storage of the two components within a single containerconsisting of a plurality of intercommunicating chambers, butaseptically isolated from the outside atmosphere,

opening of the container for the liquid component within one of the saidchambers, out of direct communication with the outside air,

the creation of a negative pressure within the chamber containing thepowder component,

suction of the liquid component, by suction due to the said negativepressure, into the chamber containing the powder component, the twochambers being kept isolated from the outside air,

mixing of the two components by agitation of the container,

compaction of the cement paste so obtained by compression thereof withpossible further aspiration of air by means of a vacuum-producinginstallation,

the possibility of fitting of a cannula in order that the emerging pastemay be better directed,

extrusion of the paste by manual or mechanical or pneumatic action on aplunger, and direct in situ emplacement of the cement.

Bearing in mind that identical reference numerals correspond toidentical or equivalent parts in the drawings, with reference to FIGS. 1and 2 it will be noted that the apparatus for implementing the processaccording to the invention comprises a substantially cylindrical hollowbody 11, a cover 12 and a plunger 13 which can mover axially betweenchamber 14 consisting of the cylindrical cavity formed in said body 11and cover 12.

The longitudinal axis of the said cylindrical cavity coincides with thelongitudinal axis 19 of the entire apparatus. Body 11 has a hollowcylindrical needle 16 fitted with a sealing plug 17 projecting outwardlyfrom the base of the said cavity.

Cover 12 has a lower part 12' which can be screwed between the said bodyand an upper cylindrically shaped externally knurled part 12" having anexternal diameter which is slightly greater than the external diameterof body 11.

The said cover also has a threaded hole 18 coaxial with saidlongitudinal axis 19, within which stem 20 of plunger 13 can moveaxially so that its central threaded portion can be screwed up or sothat its two terminal smooth cylindrical portions can slide. The saidstem also has a cavity 21 which can be closed by plug 26 to form achamber communicating with the outside atmosphere through an air intakefitted with an antibacterial filter 39 consisting of an aperture 28coaxial with the longitudinal axis of said plug 26 and four apertures 24made in the base of cavity 21.

Container 22 of the liquid component of the bone cement is housed withincavity 21, which is provided internally with means for breakingcontainer 22.

In the embodiment illustrated in FIGS. 1 to 5, container 22 is in theform of a glass vial, while the means for breaking the containercomprise a cylinder 23. This cylinder 23 has a through cylindricalaperture 34 with a longitudinal axis which converges with thelongitudinal axis of the cylinder towards the base. The said cylinderacts together with plug 26, which is movable in an axial direction withrespect to stem 20. In order to break the glass vial all that isnecessary is to press plug 26 downwards so that it in turn presses thebase of the vial downwards, forcing the lower spindle-shaped extremityof the vial to slide along the inner wall of said aperture 34.

Because aperture 34 is not coaxial with the longitudinal axis of thevial, the spindle-shaped end of the vial is forced to move laterally. Inthis way the axial pressure on plug 26 is converted into a bendingmoment applied to the base of the collar of the vial, in a previouslyweakened annular area 33.

Cylinder 23 is provided at each end with four radial channels 36 at 90°intervals connected in pairs for four channels 36' located on thelateral surface of the cylinder and running parallel to the longitudinalaxis thereof. The said channels have the function of assisting passageof the liquid from the zone above cylinder 23 to the zone below it whenthe vial breaks.

Chamber 14, which forms the aseptic container for the powder componentof the bone cement, and chamber 21 within the stem of plunger 13 areplaced in mutual communication by means of four apertures on holes 24located on the head 25 of the said plunger. These holes are protected bya filter 27 housed in the base of the cavity in the said plunger so asto prevent fragments of glass passing from chamber 21 within the stem ofthe plunger into the chamber beneath which the powder component of thecement is contained.

The stages required in order to obtain a cement paste which is ready tobe directly emplaced by the apparatus to which the invention relateswill now be illustrated.

The person preparing the cement for the surgeon initially removes adevice which is sterile in all its parts, already arranged asillustrated for example in FIG. 2, from an aseptic container. In thisembodiment of the apparatus according to the invention, container 22 ofthe liquid cement component consists of a substantially cylindricalglass vial with a slightly concave end 22' and another end elongatedoutwardly to form a point 22". Close to the base of point 22" there isprovided a zone 33 of annular weakening, so that the vial will break ina predetermined manner.

The device for breaking the vial consists of a cylinder 23 of the typeillustrated above, located at the base of cavity 21 in the stem ofplunger 13, separated from the head 25 of the plunger by a protectivefilter 27.

The vial is inserted in cavity 21 with its end 22' upwards, and point22" inserted in hole 34 of cylinder 23. Plug 26 is in a raised positionwith respect to contact plane 35 within stem 20, but pressure is gentlyapplied to the top 22' of the vial so that the pressure exerted on plug26 in a downward direction causes a bending moment to be produced in thebase of point 22" of the said vial.

The stem of plunger 13 is inserted in hole 18 of cover 12 with the lowerend of the threaded portion just engaging the thread in said hole 18. Inthis way, head 25 of the plunger together with cavity 14 in body 11bounds a chamber which acts as a container for the powder component ofthe cement.

At the lower end of body 11, a plug 17 is screwed onto needle 16 whichprojects from the body itself.

Internally, extending from its base, this plug has a cylindricalprojection 17' of diameter corresponding to the internal diameter ofsaid needle 16, so as to prevent firstly the powder component and thenthe paste contained in body 11 from obstructing needle 16. Within plug17, at its base, there is provided a seal 32 which ensures that the plugremains tight when it is screwed down onto needle 16.

With means arranged as illustrated, the operator begins the stage ofpreparing the bone cement paste, by first exerting a pressure downwardson the top of plug 26. As a result of such pressure, plug 26 pushes thevial downwards, and this, being constrained to slide with point 22" inhole 34 of cylinder 23, breaks through bending in predetermined zone 33.As illustrated in Fig. 3, following this breakage, the liquid componentbegins to fall by gravity, first through hole 34 and channels 36, andthen filter 27 and holes 24, coming into contact with the powder presentin the underlying chamber. The time necessary for falling by gravityalone would however be too long so the operator draws plunger 13upwards, as illustrated in FIG. 4, thus setting up a negative pressurein the chamber containing the powder component so that liquid is suckedinto the said chamber very quickly. The operator then shakes the entiredevice repeatedly in order to assist the reaction between the twocomponents and to obtain a more homogeneous paste.

The operator then orientates the device so that plug 17 is at the top,and then removes the said plug and screws a threaded connection 37 ontoneedle 16 of body 11 in order to attach a flexible cannula 38 of such alength that it reaches the anatomical sites involved in the operationwhen the paste is emplaced. Holding the device with cannula 38 pointingupwards he pushes the plunger upwards to that most of the air containedwithin the device is expelled.

At this point the operator, with the device positioned as shown in FIG.5, is ready to deliver a perfectly aseptic bone cement, which is notstratified and which has minimum porosity, directly in situ. In fact,extrusion through needle 16 produces greater compactness in the paste,reducing the bubbles produced by air and the vapours of the liquidcomponent by compression.

It is clear that in cases where the area into which the cement has to beextruded is easily accessible, extrusion is performed without fittingcannula 38.

Threading of the central portion of the stem 20 of plunger 13 takesplace during the extrusion stage, and this, when engaged with the threadin hole 18 of cover 12, makes it possible for the cement paste to beextruded with ease and without excessive effort, despite its highviscosity.

Although not illustrated in the drawings, paste extrusion may bemechanical instead of manual, effected through an external device, forexample a rack, which by connecting body 11 or cover 12 to the plunger,moves the latter longitudinally, in order to reduce effort by theoperator. This plunger may also be moved by a pneumatic deviceexternally connecting body 11 or cover 12 to the plunger itself. It isclear that the device must be modified in such cases, eliminating thecentral threaded portion of stem 20 of plunger 13 so that this can movefreely within hole 34, which is also not threaded, of cover 12.

Although not illustrated in the drawings, a connection valve forconnection to a vacuum unit may be fitted to the base of body 11 closeto needle 16 so as to achieve greater removal of air and therefore lessporosity in the cement.

From what has been described above, it will be clear that at no timeduring the stages in the preparation of the cement paste can theoperator inhale harmful vapours of the liquid component of the cement,given that these always remain within the internal chambers of thedevice itself during all the various stages.

FIG. 6 illustrates a second embodiment of the invention which differsfrom the first in some aspects relating to shape, which improve thehandleability of the device, such as the shape of the grip 29 forplunger 13, the shape of plug 26, which now only projects minimally fromthe grip, the shape of head 25 of the plunger itself, which is nowprovided with holes 24' which are hollowed out at the lower end in orderto aid the outflow of liquid from chamber 21, and the external knurlingon cover 12 and part of body 11. Also the two embodiments differ in themanner in which the various constituent parts of the device areconnected together.

In the second embodiment of the invention, cover 12 is in fact attachedto body 11, the former being partly inserted into the latter underpressure, while plug 17, instead of being screwed onto needle 16 of body11, is attached to the said needle by means of a bayonet attachmentwhich is itself known.

The vacuum pump VP can be connected to the plug 17 via an air sucking SDprovided with an inlet connection 1C. The plug comprises a (Luer cone)pipe union LC designed to receive the inlet connection 1C, and a sealinggasket SG.

Integers:

Vacuum pump VP

sucking duct SD

inlet connection 1C

Luer cone pipe union LC

sealing gasket SG

FIG. 7 illustrates an alternative embodiment of the apparatus accordingto the invention, in which the bending moment which causes breakage ofthe glass vial containing the liquid component is achieved by cylinder23 acting in concert with a push button 40 which projects into cavity 12of plunger 13 and can be displaced from the outside in a directionperpendicular to the longitudinal axis of the said vial. While cylinder23 has the function of jamming the point of the vial against hole 34,push button 40 can be used to displace the vial laterally and thus toproduce the bending moment necessary for breakage of the vial. This pushbutton, which is located on the lateral wall of plunger 13 close to grip29 of the plunger itself, is provided with a seal 41 which preventsexternal air from entering into stem 20 and escape of the toxic vapoursof the liquid component.

A fourth embodiment of the apparatus according to the inventionillustrated in FIG. 8, provides for the use of containers 22 for theliquid component consisting of a substantially cylindrical glass vialfitted with two longitudinally outwardly elongated points of the typedescribed above. The means for breakage of the said vial consists of acylinder 23, already illustrated, which acts together with plug 26'.This plug can be displaced from the exterior in a longitudinal directionand has at its lower end a cylindrical hole 42 which is offset withrespect to the longitudinal axis of plug 26', in the same way as hole 34of said cylinder 23.

When plug 26' is pushed downwards both the points are stressed by abending moment which breaks the vial at two predetermined points.

A fifth embodiment of this means according to the invention illustratedin FIG. 9, provides for the use of containers 22 for the liquidcomponent consisting of a cylinder of metal or plastics materialinternally coated with a material which does not react with the liquidcontained. The device for breaking the container consist of cylinder 43of diameter corresponding to the diameter of the cavity in the stem ofplunger 13, located at the base of cavity 21 behind filter 27 andprovided with an upwardly facing cutting point 44 which is capable ofperforating the lower end of the said cylinder, and by plug 26" ofchamber 21, which has a second downwardly facing point 45 alongsidecavity 21 which perforates the upper end of the said cylinder. Breakageof both the ends of container 22 takes place through the joint action ofsaid cylinder 43 and plug 26" when the plug is pushed against the saidcontainer in a longitudinal direction from the exterior.

As a result of breakage of both the ends of the container of liquidcomponent the latter falls more quickly through gravity.

Although not illustrated in the drawings, container 22 for the liquidcomponent may consist of an envelope of plastics material internallycoated with a material which does not react with the liquid component.In this case, the envelope which is provided with two rigid cylindricalunits at its ends is housed in cavity 21 of plunger 13. The first ofthese cylindrical ends is located on the base of cavity 21 wheresuitable guides prevent this from rotating with respect to the plungeritself. The second cylindrical member consists of said plug 26, which byprojecting from grip 29 enables the operator to rotate it by an amountsufficient to break the envelope through torsion.

What is claimed is:
 1. A process for mixing a bone cement formed fromtwo components, one liquid and one powder, the components being separateuntil the cement is required for use, each component comprising amixture of mutually compatible components, the processcomprising:separately storing the liquid and powder components to bemixed within a container having a plurality of chambers asepticallyisolated from atmosphere; opening the container for the liquid componentlocated within one of the chambers; creating a negative pressure in thechamber containing the powder component, the negative pressure causingsuction of the liquid component into the chamber containing the powdercomponent, the two chambers being kept isolated from outside atmosphere;mixing the two components by agitation of the container; compacting thebone cement obtained by compression; and extruding the cement for directin situ emplacement of the cement.
 2. The process as claimed in claim 1further comprising the step of inserting a flexible cannula to directthe outflow of the cement.
 3. A process as claimed in claim 1 whereinthe cement is extruded by manual action.
 4. A process as claimed inclaim 1 wherein the cement is extruded by mechanical action.
 5. Aprocess as claimed in claim 1 wherein the cement is extruded bypneumatic action.
 6. A process as claimed in claim 1 wherein compactingthe cement is accompanied by further aspiration of air by means ofvacuum generating equipment.
 7. Apparatus for holding and mixing cementcomponents comprising:a body having a longitudinal axis, a base and ahollow cylindrical needle projecting outwardly from the base; a coverattachable to the body, the cover having an aperture which is coaxialwith the longitudinal axis of the body; a plunger capable ofrecipricable axial movement in the aperture and the body, the plungerhaving a stem and a head which, with the body, defines a chamber for aaseptically housing a powder component of the cement, the plungerfurther having a cavity therein for housing a container containing aliquid component of the cement; a sealing plug for attachment to theneedle; means for breaking the container when located in the cavity; aplurality of holes between the cavity and the chamber to permit thepowder component and the liquid component to be placed in mutualcommunication after the container has been broken; and a filter locatedon the head of the plunger.
 8. Apparatus as claimed in claim 7wherein:the plunger is a substantially cylindrical and hollow stem withan enlarged upper end forming a grip; the head is attached at one end ofthe stem by attachment means; a seal is located in a circular channel inthe head and seals against an inner wall of the body; the plug can bepartly inserted at an end of the cavity remote from the head andincludes air intake means and antibacterial filter protecting suchintake means; the stem has an outer surface having a central threadedportion between two smooth cylindrical portions; and the stem is axiallymovable within the aperture of the cover so that the threaded portionthereof can be threadedly engaged or the smooth portions thereof canslide.
 9. Apparatus as claimed in claim 7 wherein the stem has an outerlateral surface which is entirely cylindrical and smooth, the stem beingslidably axially movable in the aperture of the cover.
 10. Apparatus asclaimed in claim 9 wherein the plunger is moved by a mechanical device.11. Apparatus as claimed in claim 9 wherein the plunger is moved by apneumatic device.
 12. Apparatus as claimed in claim 7 wherein:thecontainer for the liquid component comprises a substantially cylindricalglass vial having one blunt end and an elongated point at another endthereof, the point being in the proximity of the base, the vial furthercomprising an annular zone of weakness; and the means for breaking thevial comprises a cylinder having a diameter substantially the same asthat of the cavity and a height less than that of the point of the glassvial, the cylinder having a through hole, the point having alongitudinal axis which is inclined relative to a longitudinal axis ofthe cylinder, said longitudinal axes of the point and cylinderintersecting near an upper end of the cylinder, whereby when the plug isdisplaced inwardly in a longitudinal direction, a bending moment isapplied to the point of the vial to break it at the zone of weakness.13. Apparatus as claimed in claim 12 wherein the cylinder is providedwith four radial channels at each of its ends spaced at substantially90° from each other, the four radial channels being connected in pairsto four longitudinal channels located on an outer surface of thecylinder and parallel to the longitudinal axis thereof.
 14. Apparatus asclaimed in claim 7 wherein:the container of the liquid componentcomprises a substantially cylindrical glass vial having two ends whichare elongated to form a point; the means for breaking acts on the twoends of the vial and comprises a cylinder located near the base of thecavity and the plug which can be inwardly displaced in a longitudinaldirection, the plug including a cylindrical hole having a longitudinalaxis which is inclined relative to a longitudinal axis of the plug, thelongitudinal axes of the cylindrical hole and the plug intersecting neara lower end of the plug.
 15. Apparatus as claimed in claim 14 whereinthe means for breaking the vial further comprises a push buttonprojecting into the cavity of the plunger, the push button beingdisplaceable from outside the apparatus in a direction perpendicular tothe longitudinal axis of the vial, the push button being located in anupper portion of the stem and within a hole thereof, said hole beingprovided with a seal.
 16. Apparatus as claimed in claim 14 wherein thecylinder is provided with four radial channels at each of its endsspaced at substantially 90° from each other, the four radial channelsbeing connected in pairs to four longitudinal channels located on anouter surface of the cylinder and parallel to the longitudinal axisthereof.
 17. Apparatus as claimed in claim 7 wherein:the container forthe liquid component comprises a cylinder made of materialsselected-from the group comprising metals and plastics, the containerbeing internally coated with a material which does not react with theliquid component; the means for breaking the container comprises acylinder having a diameter corresponding to that of the cavity in thestem, the cylinder being provided with a first point adapted to pierce alower end of the container, the plug of the chamber including a secondpoint adapted to pierce an upper end of the container, whereby the upperand lower ends of the container are broken through joint action of thecylinder and plug when the plug is pushed against the container in alongitudinal direction.
 18. Apparatus as claimed in claim 17 wherein thecylinder is provided with four radial channels at each of its endsspaced at substantially 90° from each other, the four radial channelsbeing connected in pairs to four longitudinal channels located on anouter surface of the cylinder and parallel to the longitudinal axisthereof.